Detonating fuse



July 13, 1948. D. M. McFARLAND DETONATING FUSE Filed Feb. 26, 1946 David M. McFarland I INVENTOR.

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MWTMNM David M. McFarland, West Uhcster, ll a, i i

m G WEE to Atlas Powder @ompany, Wilmington, Del, a

corporation oi mlawara Application Fo i 28, 1946, Serial No. 65%,263

(El. lu2-27) i Clam. i

This application relates to fuse and its use.

An object of the invention is an improved detonating fuse.

Another object of the invention is an improved method for determining the presence of a break in a detonating fuse.

Other objects of the invention will be apparent from the following description.

Detonating fuse is commonly used in blasting operations as a means of initiating explosives. It is made up of a sheathed core of a detonating explosive, such ag pentaerythritol tetranitrate.

In a common method of blasting with detonating fuse, the fuse is run down a bore hole, explosive cartridges are loaded in the bore hole alongside the (use; stemming materials, such as gravel, are loaded on top of the explosive cartridges. and the fuse is then detonated, as by another line of fuse or by a blasting cap afllxed to its end. The detonating wave set u in the fuse carries detonation to the explosive in the bore hole. 1

Misilres occasionally occur when detonating fuse is employed because the fuse has been broken at some time prior to use and fails to function beyond the break. While breaks in fuse may be caused in many ways, they are most commonly caused by accidental bruising during bore hole loading operations. Sometimes the insertion or settling of explosive cartridges in a bore hole may cause breaking of fuse, but more often such breaking is caused by the loading of stemming materials, for highly abrasive substances such as gig-p, coarse stone are frequently used for stem- Since usually detonating fuse is not broken until after it has been covered up and become inaccessible, breaks can not ordinarily .be detected until after it is attempted to fire a charge and a misfire hasu'eslllted. As is well understood in the art, misfires are most disadvantageous and dangerous in blasting operations.

The present invention provides a detonating fuse and a method by means of which the presence of breaks may readily be determined prior to firing and after the fuse has been put in place.

According to the present invention a detonating fuse is provided which is made up of a train of detonating explosive sheathed in non-conductive material containing embedded therein a multiplicity of helically wound strengthening wires among which are included two helically wound insulated electrically conductive wires.

When a length of detonating fuse of the present inventionis put in place, the two insulated silver chloride cell, in series with a dArsonval electrical conductors are electrically connected together at a point to one side of a possible break. Then the electrical conductivity of the circuit including the two conductors i determined from the other side of the possible break. If a break has occurred along a length of the fuse through which the circuit'is tested, it will be shown up by the diminished conductivity of the circuit.

The invention is illustrated by the drawing. in which a specific embodiment of the invention is shown, and in which:

Figure 1 is a longitudinal view, partially cut away, of a detonating fuse of the invention;

Figure 2 is a cross sectional view of the fuse of Figure 1.

As shown in the drawings, is is a train of pentaerythritol tetranitrate: 2| is a sheath of asphalt-impregnated, waterproofed textile material; are bronze wires helically bound around sheath I! (to avoid confusion in the drawing, not all of wires 23 are numbered) 25 and 21 are channel insulated copper wires; and 29 is a waxed layer of cord binding sin'rounding wires 23 and insulated wires 25 and 21,

In one method of use of the fuse shown in the drawings, part of the covering of wires 2| and 21 is removed. These wires are stripped of insulation and twisted together, The fuse is then placed in position in a bore hole with the end bearing the twisted wires being inserted first, and the bore hole is loaded with explosive and stemming materials in the usual manner. Then when it is desired to test the fuse for breaks, the ends of the wires at the opposite end of the length of fuse wire are connected to the terminals of a blasting galvanometer, which is an instrument containing a small source of current, such as a galvanometer. Then if the fuse, and consequently, the circuit are broken at any point no deflection will ordinarily be observed on the galvanometer. When the fuse and. consequentlmthe circuit are intact, the galvanometer will show a deflection.

The detonating fuse of the invention may be provided with any convenient sheath construction. The example shown is merely for purposes of illustration.

Many different types of insulation may be used on the circuit testing wires. Usually enamel insulation is preferred, but rubber or plastic insulation, for example, may be used.

While it is preferred that both the circuit testing conductors be insulated, the invention may be used when but one of the conductors is insuiated. Furthermore, hen the conductors are protected from each other and from outside cross connection by the construction of the fuse. the

method of the invention may be used when neither circuit testing conductor is insulated.

It will sometimes be desirable to provide the circuit testing wires of weaker construction than the binding wires so thatthey will be more certain to break coincidentally with the explosive core.

The circuit testing conductors may be connected together in any practical manner. While it is usually most convenient to twist them togather as described above, they may be connected together by, for example, a pronged metal sleeve clamped over the fuse and in contact with them.

When the conductors are connected from the outside of the fuse, as by a pronged connector, it will be apparent that less than an entire length of fuse may be readily tested according to the invention.

The circuit through the conductors may be tested in any convenient manner, although it is usually preferred to use a blasting galvanometer as described above.

Sometimes when fuse of the present invention is employed in wet bore holes, it will be found that even though the fuse is broken some current will pass through the circuit due to conductivity of the medium surrounding the fuse a0 and the broken conductor ends. In such cases broken fuses can still be detected because the conductivity of the circuit in the broken fuse will test differently than the known conductivity of unbroken fuse of the same length.

It is apparent from the foregoing description that an improved fuse and method of use of fuse has been developed and that the objects of the invention have been fulfilled. It will be obvious to those skilled in the art that other embodiments than those specifically and illustratively described may be employed.

What is claimed is:

A detonating fuse comprising a train of detonating explosive surrounded by a sheath of nonconductive material and containing embedded therein a multiplicity of helically wound wires among which are included two helically wound insulated electrically conductive wires.

DAVID M. MCFARLAND.

REFERENCES CITED The following references are of record in the Name Date Schurmann July 19, 1932 Number 

